Qt 5.x and QML/OpenGL

I've written a Qt 4.8 application that makes heavy use of QGLViews and QDeclarativeViews, all living happily in WidgetLand (i.e. in dock windows, laid out in splitters, stacked in QToolBoxen etc)

With Qt 5, the replacements for those types are now windows. I am aware of QWidget::createWindowContainer() - but this breaks my ability to edit and layout my UI nicely in Qt Creator. I'm also concerned about how these embedded windows will play with stuff like, splitters, tools boxes and the like. Also it seems like keyboard focus is an issue.

It all makes me a bit wary of upgrading to Qt 5, despite the rest of the nice features.

Does anyone have any experience porting 4.8 style widgets to 5.x style windows?
Is there a way to get these to play nice with Design mode in Creator? (Some kind of wrapper widget class, that handles the gritty details of calling createWindowContainer() internally?)

What benefit do we get from having these as windows anyway? Is there any reason we couldn't have a a QQuickView window and QQuickViewWidget?